Highlight code blocks in styleguide.md

[shathor]

Problem

The styleguide doesn't use highlighting of code blocks, making it harder to read.

Solution

Use Github markdown to highlight code blocks.

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[knjk04]

Corresponding issue: #464

[shathor]

please trigger cla check again

[grimreaper]

Thank you for your contribution. Unfortunately, we’re not going to continue maintaining twitter-commons and are archiving all pull requests.